Conventionally, there are well-known a sheet supply device provided in a copier or a printer and configured to feed a sheet to an image forming section that forms an image on the sheet and a sheet supply device provided in an image reading device, such as a copier, a facsimile machine, or an image scanner and configured to feed a sheet (document) to a predetermined reading position. As a specific example of such a sheet supply device, there is known one configured to deliver a sheet on the sheet supply tray by means of a delivery roller, convey the delivered sheet to the reading position one by one by means of a separation section including a feeding roller and a separation member, and feed the read sheet to a sheet discharge tray.
Among such sheet supply devices, there is known, in a device of a type capable of handling a large volume of sheets (50 sheets or more), a sheet supply device provided with an elevating tray that elevates a downstream side of sheets placed on the sheet supply tray to bring a topmost surface of the sheet bundle into abutment against a peripheral surface of a delivery roller suspended by its own weight (see, for example, Patent Document 1). The elevating tray supports the downstream side of the sheets placed on the sheet supply tray separately from the sheet supply tray and is configured to turn about an upstream side end portion thereof by means of an actuator such as a motor or a solenoid. The elevating tray turns from a set position where a document is set to a delivery position where the topmost surface of the sheet bundle placed on the elevating tray abuts against the delivery roller.
A sheet feed operation in the sheet supply device provided with such an elevating tray is as follows. The elevating tray turns, in response to a sheet feed signal, in such a direction that the downstream side thereof is elevated to elevate the leading end side (downstream side end portion in a sheet conveying direction) of the sheet. When the topmost surface of the sheet bundle reaches the delivery position abutting against the delivery roller, the turning of the elevating tray is stopped. Then, the sheet is delivered by means of the delivery roller. The delivered sheet is conveyed one by one by the separation section to the reading position. When feeding of all the sheets on the sheet supply tray is completed, the elevating tray turns downward in a reverse direction until the downstream side thereof reaches the set position where the sheet can be placed on the sheet supply tray.